The St. Louis Adult Felony Drug Court program began in 1997 as a pre-plea drug court that accepts adults charged with drug offenses shortly after their arrest. Participation is voluntary and participants must submit to regular alcohol and drug testing, make regular court appearances, maintain employment, and complete prescribed drug and alcohol treatment. Typically, the drug court program takes about 1.5 years to complete. The first 219 adult drug court graduates, who completed drug court before 2001, were compared with a carefully matched control group of 219 individuals who pleaded guilty and entered probation rather than drug court. Data on the costs and benefits of drug court versus traditional probation were collected at the State and local levels and included wage information, welfare, Medicaid, drug and alcohol treatment, mental health treatment, criminal arrests, criminal convictions, time in jail, prison sentences, court hearings, births of drug-exposed infants, and administration and supervision in drug court and probation programs. The analysis indicated that after adding together the costs of administration, supervision, drug and alcohol treatment, court hearings, urinalysis, and pretrial detention, the average cost for one individual to complete drug court was approximately $7,793, compared to the approximately $6,344 it cost for one individual to complete probation. However, numerous benefits were observed for the drug court participants that were not observed for the probationers. Among the benefits of drug court are lower costs for jail time, lower costs for pretrial detention, higher employment wages, more months in employment, lower health and mental health care costs, shorter incarceration periods, and fewer infants born drug-exposed. The final cost-benefit analysis over a 4-year period indicated that the benefits of drug court add up to about $1,362 per individual. Thus, over a 4-year period, the total drug court cost was exceeded by its benefits. Net savings over the 4-year period after drug court completion added up to $7,707 per drug court participant, which is the amount of money that would have been paid by taxpayers had the drug court participants chosen probation instead of drug court. Figures, tables, appendix, references